1. Field of the Invention
The invention relates to pressure measuring probes and more particularly to cooled pressured probes for measuring changes in the pressure of high velocity fluid streams over the surface of an object.
2. Description of the Prior Art
Pitot-pressure probes for measuring changes in the pressure in the shock layer around a model such as a nose cone, airfoil or the like supported in super and hypersonic wind tunnels are generally known.
Typically, the hypersonic air stream is heated up to 500.degree. F. and the transducers used to measure changes in the actual or dynamic pressure in the resulting shock layer on and about the model surface must be protected from the hostile temperatures encountered to avoid thermally induced errors in the resulting pressure measurements and possible damage to the probe and transducers.
To protect against such undesirable results, the pressure transducers are either thermally insulated and mounted in the probe housing or support strut as far removed from the probe tip as possible or completely outside of the test section. Either remote transducer positioning arrangement requires a relatively long connector tube between the probe tip and pressure transducer.
This increase in tubing volume results in an increase of "settling-time" of the pressure probe, settling time is the time required for pressure changes in the fluid stream to appear at the pressure sensing transducer. As the probe tip is frequently moved relative to the model surface to permit the measurement of changes in the pressure distribution in the shock layer on and around the model, "settling-time" is critically related to the rate of relative movement and frequency at which the measurements can be taken. This must in turn meet the operating time limits of the wind tunnel in which the measurements are made.
To meet the tunnel operating time limits by controlling the "settling-time" generally results in an increases in the size of the probe tip which leads to interference errors in pressure measurements made with such a probe. To avoid interference errors, it has been found that the probe tip should be no larger than about thirty-percent (30%) of the boundary layer height in the flow around and on the test model surface. Typically the diameter of the smallest connector tubes in conventional pressure probes ranges from 0.0200d. to 0.0600d inches.